Solid-state imaging device, method of manufacturing the same, and imaging apparatus

ABSTRACT

A solid-state imaging device includes a photoelectric conversion section which is disposed on a semiconductor substrate and which photoelectrically converts incident light into signal charges, a pixel transistor section which is disposed on the semiconductor substrate and which converts signal charges read out from the photoelectric conversion section into a voltage, and an element isolation region which is disposed on the semiconductor substrate and which isolates the photoelectric conversion section from an active region in which the pixel transistor section is disposed. The pixel transistor section includes a plurality of transistors. Among the plurality of transistors, in at least one transistor in which the gate width direction of its gate electrode is oriented toward the photoelectric conversion section, at least a photoelectric conversion section side portion of the gate electrode is disposed within and on the active region with a gate insulating film therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/743,467, filed Jun. 18, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/063,235, filed Oct. 25, 2013, now U.S. Pat. No.9,142,589, which is a division of U.S. patent application Ser. No.12/614,967, filed Nov. 9, 2009, now U.S. Pat. No. 8,605,183, whichclaims priority to Japanese Patent Application No. JP 2008-289670, filedin the Japan Patent Office on Nov. 12, 2008, the entire disclosures ofwhich are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device, a methodof manufacturing the same, and an imaging apparatus.

2. Description of the Related Art

In solid-state imaging devices, image quality has been improved byincreasing the number of pixels. However, with an increase in the numberof pixels and a reduction in the size of pixels, the saturation chargeamount Qs has decreased, resulting in an increase in influence on noise.This has increased the importance of techniques for maintaining thesaturation charge amount at as high a level as possible and techniquesfor increasing conversion efficiency.

FIG. 24 shows a layout of a solid-state imaging device according to therelated art. As shown in FIG. 24, gate electrodes 22 in a pixeltransistor section 13 disposed in an active region 15 protrude over anelement isolation region 16 toward photoelectric conversion sections 12(for example, refer to Japanese Unexamined Patent ApplicationPublication No. 2003-031785, etc).

FIG. 25 shows an equivalent circuit of the solid-state imaging device.As shown in FIG. 25, a pixel section 10 includes photoelectricconversion sections 12 (12A, 12B, 12C, and 12D) composed of fourphotodiodes. The pixel transistor section 13 also includes a transfertransistor TrT, a floating diffusion (part of transfer gate pn junction)FD, a reset transistor TrR, an amplifier transistor TrA, and a selectiontransistor TrS.

In the solid-state imaging device according to the related art, the sizeof the pixel layout is increased due to protruding portions of the gateelectrodes 22 of the selection transistor TrS, the amplifier transistorTrA, the reset transistor TrS, etc., the protruding portions protrudingover the element isolation region 16 toward the photoelectric conversionsections 12.

SUMMARY OF THE INVENTION

The problem to be solved is that protruding portions of the gateelectrodes of pixel transistors increase the size of the pixel layout,the protruding portions protruding over the element isolation regiontoward the photoelectric conversion sections.

It is desirable to decrease the layout area of pixel transistors so thatthe area of each of the photoelectric conversion sections can beincreased.

According an embodiment of the present invention, a solid-state imagingdevice includes a photoelectric conversion section which is disposed ona semiconductor substrate and which photoelectrically converts incidentlight into signal charges, a pixel transistor section which is disposedon the semiconductor substrate and which converts signal charges readout from the photoelectric conversion section into a voltage, and anelement isolation region which is disposed on the semiconductorsubstrate and which isolates the photoelectric conversion section froman active region in which the pixel transistor section is disposed. Thepixel transistor section includes a plurality of transistors. Among theplurality of transistors, in at least one transistor in which the gatewidth direction of its gate electrode is oriented toward thephotoelectric conversion section, at least a photoelectric conversionsection side portion of the gate electrode is disposed within and on theactive region with a gate insulating film therebetween.

In the solid-state imaging device according to the embodiment of thepresent invention, among the plurality of transistors, in at least onetransistor in which the gate width direction of its gate electrode isoriented toward the photoelectric conversion section, its photoelectricconversion section side does not protrude over the element isolationregion and is disposed within and above the active region. Consequently,the size of the pixel transistor-forming region is reduced compared withthe case where protruding portions of gate electrodes protrude over anelement isolation region according to the related art. That is, the sizeof the photoelectric conversion section can be increased by an areacorresponding to the area occupied by protruding portions of gateelectrodes formed so as to protrude over the element isolation regionaccording to the related art, and thus the formation area of thephotoelectric conversion section can be increased.

According to another embodiment of the present invention, a method ofmanufacturing a solid-state imaging device includes the steps of formingan element isolation region on a semiconductor substrate, the elementisolation region isolating a photoelectric conversion section-formingregion from an active region in which pixel transistors are to beformed; forming a photoelectric conversion section in the photoelectricconversion section-forming region on the semiconductor substrate, thephotoelectric conversion section converting incident light intoelectrical signals; and forming a pixel transistor section in the activeregion on the semiconductor substrate, the pixel transistor sectionincluding a plurality of transistors which convert signal charges readout from the photoelectric conversion section into a voltage. When theplurality of transistors are formed, at least one transistor in whichthe gate width direction of its gate electrode is oriented toward thephotoelectric conversion section is formed such that at least aphotoelectric conversion section side portion of the gate electrode isdisposed within and on the active region with a gate insulating filmtherebetween.

In the method of manufacturing a solid-state imaging device according tothe other embodiment of the present invention, among the plurality oftransistors, at least one transistor in which the gate width directionof its gate electrode is oriented toward the photoelectric conversionsection is formed such that a photoelectric conversion section sideportion of the gate electrode is disposed within and above the activeregion. Consequently, the size of the pixel transistor-forming region isreduced compared with the case where protruding portions of gateelectrodes protrude over an element isolation region according to therelated art. That is, the size of the photoelectric conversion sectioncan be increased by an area corresponding to the area occupied byprotruding portions of gate electrodes formed so as to protrude over theelement isolation region according to the related art, and thus theformation area of the photoelectric conversion section can be increased.

According to another embodiment of the present invention, an imagingapparatus includes a focusing optical device which focuses incidentlight, a solid-state imaging device which receives light focused by thefocusing optical device and photoelectrically converts the light, and asignal processing device which processes photoelectrically convertedsignals. The solid-state imaging device includes a photoelectricconversion section which is disposed on a semiconductor substrate andwhich photoelectrically converts incident light into signal charges, apixel transistor section which is disposed on the semiconductorsubstrate and which converts signal charges read out from thephotoelectric conversion section into a voltage, and an elementisolation region which is disposed on the semiconductor substrate andwhich isolates the photoelectric conversion section from an activeregion in which the pixel transistor section is disposed. The pixeltransistor section includes a plurality of transistors. Among theplurality of transistors, in at least one transistor in which the gatewidth direction of its gate electrode is oriented toward thephotoelectric conversion section, at least a photoelectric conversionsection side portion of the gate electrode is disposed within and on theactive region with a gate insulating film therebetween.

In the imaging apparatus according to the other embodiment of thepresent invention, since the solid-state imaging device according to theembodiment of the present invention is included, the size of thephotoelectric conversion section can be increased by an areacorresponding to the area occupied by protruding portions of gateelectrodes formed so as to protrude over the element isolation regionaccording to the related art, and thus the formation area of thephotoelectric conversion section can be increased.

The solid-state imaging device according to the embodiment of thepresent invention is advantageous in that, since the formation area ofthe photoelectric conversion section can be increased, the saturationcharge amount can be increased. Furthermore, since the gate capacitanceof pixel transistors can be decreased, conversion efficiency can beincreased.

The method of manufacturing a solid-state imaging device according tothe other embodiment of the present invention is advantageous in that,since the formation area of the photoelectric conversion section can beincreased, the saturation charge amount can be increased. Furthermore,since the gate capacitance of pixel transistors can be decreased,conversion efficiency can be increased.

The imaging apparatus according to the other embodiment of the presentinvention is advantageous in that, since the formation area of thephotoelectric conversion section can be increased, the saturation chargeamount can be increased. Furthermore, since the gate capacitance ofpixel transistors can be decreased, conversion efficiency can beincreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional plan view showing a first example of asolid-state imaging device according to a first embodiment, FIG. 1B is across-sectional view taken along the line IB-IB of FIG. 1A, and FIG. 1Cis a cross-sectional view taken along the line IC-IC of FIG. 1A;

FIG. 2 is a schematic cross-sectional view of a solid-state imagingdevice according to the related art, showing a problem associated withthe related art;

FIG. 3 is a schematic cross-sectional view showing a modificationexample of the first example of a structure of a solid-state imagingdevice;

FIG. 4A is a cross-sectional plan view showing an example of asolid-state imaging device according to a second embodiment, and FIG. 4Bis a cross-sectional view taken along the line IVB-IVB of FIG. 4A;

FIG. 5A is a cross-sectional view taken along the line VA-VA of FIG. 4A,and FIG. 5B is a cross-sectional view taken along the line VB-VB of FIG.4A;

FIG. 6 is a cross-sectional plan view showing an example of asolid-state imaging device according to a third embodiment;

FIG. 7 is a cross-sectional view showing a step in a method ofmanufacturing a solid-state imaging device according to a fourthembodiment;

FIG. 8 is a cross-sectional view showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIG. 9 is a cross-sectional view showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIG. 10 is a cross-sectional view showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIG. 11 is a cross-sectional view showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIG. 12 is a cross-sectional view showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIG. 13 is a cross-sectional view showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIGS. 14A and 14B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIGS. 15A and 15B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIGS. 16A and 16B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIGS. 17A and 17B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIGS. 18A and 18B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIGS. 19A and 19B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIGS. 20A and 20B include cross-sectional views showing steps in themethod of manufacturing a solid-state imaging device according to thefourth embodiment;

FIG. 21 includes cross-sectional views showing a step in the method ofmanufacturing a solid-state imaging device according to the fourthembodiment;

FIG. 22 includes cross-sectional views showing a step in a method ofmanufacturing a solid-state imaging device according to a fifthembodiment;

FIG. 23 is a block diagram showing an example of an imaging apparatusaccording to a sixth embodiment;

FIG. 24 is a plan view showing a layout of an example of a solid-stateimaging device according to the related art; and

FIG. 25 is an equivalent circuit of the solid-state imaging deviceaccording to the related art shown in FIG. 24.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedbelow.

First Embodiment First Example of Structure of Solid-State ImagingDevice

A first example of a structure of a solid-state imaging device accordingto a first embodiment of the present invention will be described withreference to FIGS. 1A to 1C. FIG. 1A is a cross-sectional plan viewshowing a layout of a solid-state imaging device 1, FIG. 1B is across-sectional view taken along the line IB-IB of FIG. 1A, and FIG. 1Cis a cross-sectional view taken along the line IC-IC of FIG. 1A.

As shown in FIGS. 1A to 1C, a plurality of photoelectric conversionsections 12 (e.g., photoelectric conversion sections 12A, 12B, 12C, and12D) and a pixel transistor section 13 are disposed on a semiconductorsubstrate 11. Each of the photoelectric conversion sections 12photoelectrically converts incident light into signal charges, and forexample, includes a p-type region and an n-type region disposedthereunder.

A floating diffusion FD is disposed on the semiconductor substrate 11 incentral portions of the photoelectric conversion sections 12A, 12B, 12C,and 12D. The floating diffusion FD is, for example, composed of ann-type diffusion layer. A contact region 61 is disposed in the center ofthe floating diffusion FD.

Furthermore, between each of the photoelectric conversion sections 12and the floating diffusion FD, a transfer gate electrode 21 of atransfer transistor TrT is disposed on the semiconductor substrate 11with a gate insulating film (not shown) therebetween.

The pixel transistor section 13 converts signal charges read out fromthe photoelectric conversion sections 12 by the transfer gate electrodes21 into a voltage, and for example, includes a plurality of transistorsin a p-well active region 15 disposed on the semiconductor substrate 11.The plurality of transistors, for example, include a reset transistorTrR, an amplifier transistor TrA, and a selection transistor TrS.

For example, among the gate electrodes 22 (22R, 22A, and 22S) of theplurality of transistors, in at least one gate electrode 22, the gatewidth direction is oriented toward the photoelectric conversion sections12.

In this embodiment, in each of the gate electrode 22R of the resettransistor TrR, the gate electrode 22A of the amplifier transistor TrA,and the gate electrode 22S of the selection transistor TrS, the gatewidth direction is oriented toward the photoelectric conversion sections12.

An element isolation region 16 which isolates the photoelectricconversion sections 12 from the active region 15 is disposed on thesemiconductor substrate 11. The element isolation region 16, forexample, has a shallow trench isolation (STI) structure.

In each of the gate electrodes 22R, 22A, and 22S, at least aphotoelectric conversion section side portion is disposed within andabove the active region 15.

Furthermore, a sidewall insulation film 23 is disposed on each sidewallof each of the gate electrodes 22 (22R, 22A, and 22S). The sidewallinsulation films 23 (23A and 23B) disposed on both sidewalls parallel tothe gate length direction of each of the gate electrodes 22 (22R, 22A,and 22S) extend over the boundary between the active region 15 and theelement isolation region 16.

Furthermore, source/drain regions 24 and 25, which are separated fromeach other, are disposed in the active region 15 at both sides of thegate electrode 22S. Similarly, source/drain regions (not shown), whichare separated from each other, are disposed in the active region 15 atboth sides of each of the gate electrodes 22R and 22A.

In this embodiment, a source/drain region (on the right side of the gateelectrode 22R) of the reset transistor TrR and a source/drain region (onthe left side of the gate electrode 22A) of the amplifier transistor TrAare composed of a common diffusion layer. Furthermore, anothersource/drain region (on the right side of the gate electrode 22A) of theamplifier transistor TrA and a source/drain region of the selectiontransistor TrS are composed of a common diffusion layer.

Although not shown, on the semiconductor substrate 11, the photoelectricconversion sections 12 and the pixel transistor section 13 constitute apixel section, and a peripheral circuit section is disposed in theperiphery of the pixel section, the peripheral circuit sectionincluding, for example, a horizontal scanning circuit, a verticalscanning circuit for pixels, a pixel driving circuit, a timing generatorcircuit, etc.

The solid-state imaging device 1 is thus constituted.

In the solid-state imaging device 1, gate width directions of the gateelectrodes 22 (22R, 22A, and 22S) of a plurality of transistors areoriented toward the photoelectric conversion sections 12. In each of thegate electrodes 22R, 22A, and 22S, its photoelectric conversion section12 side does not protrude over the element isolation region 16 and isdisposed within and above the active region 15. Consequently, the sizeof the pixel transistor-forming region is reduced compared with the casewhere protruding portions of gate electrodes protrude over an elementisolation region according to the related art. That is, the size of thephotoelectric conversion sections 12 can be increased by an areacorresponding to the area occupied by protruding portions of gateelectrodes formed so as to protrude over the element isolation regionaccording to the related art, and thus the formation area of thephotoelectric conversion sections 12 can be increased.

Since the formation area of the photoelectric conversion sections 12 canbe increased, it is possible to solve the problem that, at a given pixelsize, the area of the photoelectric conversion section 12 is reduced byan amount corresponding to protruding portions of the gate electrodes 22protruding toward the element isolation region 16.

Consequently, the saturation charge amount can be increased, which isadvantageous.

Furthermore, since the formation area of the photoelectric conversionsections 12 can be increased, the gate capacitance of the pixeltransistors can be decreased. Therefore, it is possible to solve theproblem that the parasitic capacitance increases by an amountcorresponding to protruding portions of the gate electrodes 22protruding toward the element isolation region 16.

Consequently, conversion efficiency can be increased, which isadvantageous.

Furthermore, referring to FIG. 2, in a solid-state imaging deviceaccording to the related art, as a comparative example, a gate electricfield is applied to portions of a gate electrode 22 disposed on theelement isolation region 16 sides of the boundaries between the activeregion 15 and the element isolation region 16 having an STI structure,and therefore, there is concern regarding the action of parasitictransistors. That is, due to the gate electric field, electrons areinduced to move under the element isolation region 16 beneath the gateelectrode 22, resulting in white spots/dark current. Furthermore, bydecreasing the depth of the element isolation region 16, the stress inthe element isolation region 16 is reduced, and thereby it is possibleto improve white spots/dark current caused by stress. However, if thedepth of the element isolation region 16 is decreased, electrons fromthe gate electric field are induced to move under the element isolationregion 16, thus decreasing the effect of improving white spots/darkcurrent.

As described above, parasitic transistors may cause the deterioration ofdark current. In order to suppress the dark current, there is no choicebut to increase the substrate concentration (P⁻). When optimization isperformed, N⁻ in an N⁻-type region at the junction of the N⁻-type regionand the P-type region in the photoelectric conversion section 12 iscounteracted by the increase in P. Thereby, the area of the actualphotoelectric conversion section 12 decreases from the designed value,resulting in a decrease in sensitivity.

However, in the solid-state imaging device 1 according to the embodimentof the present invention, since the gate electrodes 22R, 22A, and 22S donot protrude over the element isolation region 16, the action ofparasitic transistors can be prevented.

Consequently, generation of dark current can be reduced, and sensitivitycan be improved.

In the example described above, the gate electrodes 22R, 22A, and 22Sdisposed on the active region 15 are located within the active region15. Similarly, in terms of the layout, by forming the triangle-shapedtransfer gate electrodes 21 of the transfer transistors TrT so as not toprotrude over the element isolation region 16, the formation area of thephotoelectric conversion sections 12 can be increased. That is, thetransfer gate electrodes 21 are formed so as to be located on and withinthe photoelectric conversion section 12.

In this embodiment, when alignment is taken into consideration, theamount of overlap Y1 is defined according to the equation (1):

Y1=√(x1²+(ΔW/2)²+(ΔL/2)²)

wherein x1 represents the alignment accuracy between the active region15 and the gate electrode 22, ΔW represents the variation in the widthof the element isolation region 16, and ΔL represents the variation inthe width of the gate electrode 22. Furthermore, the amount of overlapbetween the gate electrode 22 and the element isolation region 16 isrepresented by Y, and the width of the sidewall insulation film 23 isrepresented by Z.

When alignment is not taken into consideration, the amount of overlap Y2is defined according to the equation (2):

Y2=√((ΔW/2)²+(ΔL/2)²)

The embodiment of the present invention is possible, for example, evenif Y2≦Y≦Y1 and x1≦Z.

That is, even if there are variations in the alignment and the finishedwidth of each of the element isolation region 16, the gate electrode 22,the sidewall insulation film 23, etc., the embodiment of the presentinvention is possible as long as at least the sidewall insulation film23 overlaps the element isolation region 16 and the source/drain regions24 and 25 are separated from each other.

In a wafer or a chip, at least some of the sidewall insulation films 23should be in a state shown in FIG. 1B. That is, within the ranges of theconditions described above, by reducing the alignment margin and thefinished width margin, the amount of protrusion of the gate electrode 22toward the element isolation region 16 is minimized.

By using the layout in which some of sidewall insulation films 23overlap the element isolation region 16, the effect described above canbe produced. Furthermore, the width of the sidewall insulation film 23can be optimized within the ranges of the conditions described above.

(Modification Example of First Example of Structure of Solid-StateImaging Device)

As shown in FIG. 3, in a cross-section taken along the gate widthdirection, the solid-state imaging device 1, for example, may be formedsuch that one of the sidewall insulation films 23 extends over theboundary between the element isolation region 16 and the active region15. That is, an end of the gate electrode 22 located on one sidewallinsulation film 23 side is disposed within and above the active region15. An end of the gate electrode 22 located on another sidewallinsulation film 23 side is disposed so as to protrude over the elementisolation region 16. The solid-state imaging device 1 according to theembodiment of the present invention also includes such a structure.

Second Embodiment Second Example of Structure of Solid-State ImagingDevice

An example of a structure of a solid-state imaging device according to asecond embodiment of the present invention will be described withreference to FIGS. 4A and 4B and FIGS. 5A and 5B. FIG. 4A is across-sectional plan view showing a layout of a solid-state imagingdevice 2, FIG. 4B is a cross-sectional view taken along the line IVB-IVBof FIG. 4A, FIG. 5A is a cross-sectional view taken along the line VA-VAof FIG. 4A, and FIG. 5B is a cross-sectional view taken along the lineVB-VB of FIG. 4A.

As shown in FIGS. 4A to 5B, the solid-state imaging device 2 is the sameas the solid-state imaging device 1 except that LDD regions 26 and 27are disposed in the pixel transistor section 13 of the solid-stateimaging device 1.

That is, a plurality of photoelectric conversion sections 12 (e.g.,photoelectric conversion sections 12A, 12B, 12C, and 12D) and a pixeltransistor section 13 are disposed on a semiconductor substrate 11. Afloating diffusion FD is disposed on the semiconductor substrate 11 incentral portions of the photoelectric conversion sections 12.Furthermore, between each of the photoelectric conversion sections 12and the floating diffusion FD, a transfer gate electrode 21 of atransfer transistor TrT is disposed on the semiconductor substrate 11with a gate insulating film 20 therebetween.

The pixel transistor section 13 includes a plurality of transistors in ap-well active region 15 disposed on the semiconductor substrate 11. Theplurality of transistors, for example, include a reset transistor TrR,an amplifier transistor TrA, and a selection transistor TrS.

Among the gate electrodes 22 (22R, 22A, and 22S) of the plurality oftransistors, in at least one gate electrode 22, the gate width directionis oriented toward the photoelectric conversion sections 12. In thisembodiment, in each of the gate electrode 22R of the reset transistorTrR, the gate electrode 22A of the amplifier transistor TrA, and thegate electrode 22S of the selection transistor TrS, the gate widthdirection is oriented toward the photoelectric conversion sections 12.

An element isolation region 16 which isolates the photoelectricconversion sections 12 from the active region 15 is disposed on thesemiconductor substrate 11. The element isolation region 16, forexample, has a shallow trench isolation (STI) structure.

In each of the gate electrodes 22R, 22A, and 22S, at least aphotoelectric conversion section side portion is disposed within and onthe active region 15 with the gate insulating film 20 therebetween.

Furthermore, a sidewall insulation film 23 is disposed on each sidewallof each of the gate electrodes 22 (22R, 22A, and 22S). The sidewallinsulation films 23 (23A and 23B) disposed on both sidewalls parallel tothe gate length direction of each of the gate electrodes 22R, 22A, and22S extend over the boundary between the active region 15 and theelement isolation region 16.

Furthermore, source/drain regions 24 and 25, which are separated fromeach other, are disposed in the active region 15 at both sides of thegate electrode 22S. Similarly, source/drain regions (not shown), whichare separated from each other, are disposed in the active region 15 atboth sides of each of the gate electrodes 22R and 22A.

In this embodiment, a source/drain region of the reset transistor TrRand a source/drain region of the amplifier transistor TrA are composedof a common diffusion layer. Furthermore, another source/drain region ofthe amplifier transistor TrA and a source/drain region of the selectiontransistor TrS are composed of a common diffusion layer.

Furthermore, LDD regions 26 and 27, which are separated from each other,are disposed in the active region 15 under the sidewall insulation films23 (23A and 23B) disposed on both sidewalls parallel to the gate widthdirection of each of the gate electrodes 22. Accordingly, thesource/drain region 24 is disposed in the active region 15 located onone side of the gate electrode 22 with the LDD region 26 therebetween,and the source/drain region 25 is disposed in the active region 15 onthe other side of the gate electrode 22 with the LDD region 27therebetween. The LDD regions 26 and 27 have a lower impurityconcentration than the source/drain regions 24 and 25.

Although not shown, on the semiconductor substrate 11, the photoelectricconversion sections 12 and the pixel transistor section 13 constitute apixel section, and a peripheral circuit section is disposed in theperiphery of the pixel section, the peripheral circuit sectionincluding, for example, a horizontal scanning circuit, a verticalscanning circuit for pixels, a pixel driving circuit, a timing generatorcircuit, etc.

The solid-state imaging device 2 is thus constituted.

In the solid-state imaging device 2, the same working-effects as thoseof the solid-state imaging device 1 can be obtained. Furthermore, sinceLDD regions 26 and 27 are disposed in the pixel transistor section, theelectric field at the drain end is lowered.

In the example described above, the gate electrodes 22R, 22A, and 22Sdisposed on the active region 15 are located within the active region15. Similarly, in terms of the layout, by forming the triangle-shapedtransfer gate electrodes 21 of the transfer transistors TrT so as not toprotrude over the element isolation region 16, the formation area of thephotoelectric conversion sections 12 can be increased. That is, thetransfer gate electrodes 21 are formed so as to be located on and withinthe photoelectric conversion section 12.

Third Embodiment Third Example of Structure of Solid-State ImagingDevice

An example of a structure of a solid-state imaging device according to athird embodiment of the present invention will be described withreference to FIG. 6 which is a cross-sectional plan view.

As shown in FIG. 6, a plurality of photoelectric conversion sections 12(e.g., photoelectric conversion sections 12A, 12B, 12C, and 12D) and apixel transistor section 13 are disposed on a semiconductor substrate11. Each of the photoelectric conversion sections 12 photoelectricallyconverts incident light into signal charges, and for example, includes ap-type region and an n-type region disposed thereunder.

A floating diffusion FD is disposed on the semiconductor substrate 11 incentral portions of the photoelectric conversion sections 12A, 12B, 12C,and 12D. The floating diffusion FD is, for example, composed of ann-type diffusion layer.

Furthermore, between each of the photoelectric conversion sections 12and the floating diffusion FD, a transfer gate electrode 21 of atransfer transistor TrT is disposed on the semiconductor substrate 11with a gate insulating film therebetween.

The pixel transistor section 13 converts signal charges read out fromthe photoelectric conversion sections 12 by the transfer gate electrodes21 into a voltage, and for example, includes a plurality of transistorsin a p-well active region 15 disposed on the semiconductor substrate 11.The plurality of transistors, for example, include a reset transistorTrR, an amplifier transistor TrA, and a selection transistor TrS.

For example, among the gate electrodes 22 (22R, 22A, and 22S) of theplurality of transistors, in at least one gate electrode 22, the gatewidth direction is oriented toward the photoelectric conversion sections12.

In this embodiment, in each of the gate electrode 22R of the resettransistor TrR, the gate electrode 22A of the amplifier transistor TrA,and the gate electrode 22S of the selection transistor TrS, the gatewidth direction is oriented toward the photoelectric conversion sections12.

An element isolation region 16 which isolates the photoelectricconversion sections 12 from the active region 15 is disposed on thesemiconductor substrate 11. The element isolation region 16, forexample, has a shallow trench isolation (STI) structure.

In each of the gate electrodes 22R and 22S, at least a photoelectricconversion section 12 side is disposed within and on the active region15 with a gate insulating film therebetween. The gate electrode 22A isdisposed on the active region 15 with a gate insulating filmtherebetween so as to protrude toward the element isolation region 16.

Furthermore, as in the description with reference to FIG. 1, a sidewallinsulation film 23 is disposed on each sidewall of each of the gateelectrodes 22R, 22A, and 22S. The sidewall insulation films 23 (23A and23B) disposed on both sidewalls parallel to the gate length direction ofeach of the gate electrodes 22R and 22S extend over the boundary betweenthe active region 15 and the element isolation region 16.

Furthermore, as in the description with reference to FIG. 1,source/drain regions 24 and 25, which are separated from each other, aredisposed in the active region 15 at both sides of the gate electrode22S. Similarly, source/drain regions (not shown), which are separatedfrom each other, are disposed in the active region 15 at both sides ofeach of the gate electrodes 22R and 22A.

Furthermore, as in the description with reference to FIG. 5B, LDDregions 26 and 27, which are separated from each other, may be disposedin the active region 15 under the sidewall insulation films 23 (23A and23B) disposed on both sidewalls parallel to the gate width direction ofeach of the gate electrodes 22, the LDD regions 26 and 27 having a lowerimpurity concentration than the source/drain regions 24 and 25.Accordingly, the source/drain region 24 is disposed in the active region15 located on one side of the gate electrode 22 with the LDD region 26therebetween, and the source/drain region 25 is disposed in the activeregion 15 on the other side of the gate electrode 22 with the LDD region27 therebetween.

Although not shown, on the semiconductor substrate 11, the photoelectricconversion sections 12 and the pixel transistor section 13 constitute apixel section, and a peripheral circuit section is disposed in theperiphery of the pixel section, the peripheral circuit sectionincluding, for example, a horizontal scanning circuit, a verticalscanning circuit for pixels, a pixel driving circuit, a timing generatorcircuit, etc.

The solid-state imaging device 3 is thus constituted.

In the solid-state imaging device 3, gate width directions of the gateelectrodes 22R, 22A, and 22S of a plurality of transistors are orientedtoward the photoelectric conversion sections 12. In each of the gateelectrodes 22R and 22S, its photoelectric conversion section 12 sidedoes not protrude over the element isolation region 16 and is disposedwithin and above the active region 15. Consequently, the size of thepixel transistor-forming region is reduced compared with the case whereprotruding portions of gate electrodes protrude over an elementisolation region according to the related art. That is, the size of thephotoelectric conversion sections 12 can be increased by an areacorresponding to the area occupied by protruding portions of gateelectrodes formed so as to protrude over the element isolation regionaccording to the related art, and thus the formation area of thephotoelectric conversion sections 12 can be increased.

Since the formation area of the photoelectric conversion sections 12 canbe increased, it is possible to solve the problem that, at a given pixelsize, the area of the photoelectric conversion section 12 is reduced byan amount corresponding to protruding portions of the gate electrodes 22protruding toward the element isolation region 16.

Consequently, the saturation charge amount can be increased, which isadvantageous.

Furthermore, as in the solid-state imaging device 1, since the gateelectrodes 22R and 22S do not protrude over the element isolation region16 in the solid-state imaging device 3, the action of parasitictransistors can be prevented.

Consequently, generation of dark current can be reduced, and sensitivitycan be improved.

In the solid-state imaging device 3, the gate electrode 22A of theamplifier transistor may be formed so as not to protrude over theelement isolation region. In such a case, the area of the photoelectricconversion section per unit pixel area can be increased. However, whenthe gate electrode 22A of the amplifier transistor is formed so as toprotrude over the element isolation region, the 1/f noise of theamplifier transistor can be more decreased, which may be advantageous insome cases.

Furthermore, in the amplifier transistor TrA, in order to reduce randomnoise, the larger the size of the channel-forming region, the better. Asthe size of the channel-forming region is increased, the region is mademore even and noise is more reduced. Consequently, in the amplifiertransistor TrA, the amount protrusion of the portion protruding over theelement isolation region 16 is the same as that in the related art, andthus the channel area is increased. In the meantime, in the resettransistor TrR and the selection transistor TrS which are less affectedby noise, protrusion of the gate electrodes 22R and 22S may bedecreased. That is, a structure may be employed in which the sidewallinsulation films of the gate electrodes extend over the elementisolation region 16.

Consequently, in the solid-state imaging device 3, by increasing thearea of the photoelectric conversion section 12 relative to the relatedart, it is possible obtain pixel characteristics in which random noisedoes not deteriorate.

Fourth Embodiment First Example of Method of Manufacturing Solid-StateImaging Device

An example of a method of manufacturing a solid-state imaging deviceaccording to an embodiment of the present invention will be describedwith reference to FIGS. 7 to 21 which are cross-sectional views.

Referring to FIG. 7, as a semiconductor substrate 11, for example, asilicon substrate is used. A pad oxide film 111 and a silicon nitridefilm 112 are formed on the semiconductor substrate 11. The pad oxidefilm 111 is formed by oxidizing the surface of the semiconductorsubstrate 11, for example, by thermal oxidation. The pad oxide film 111is formed, for example, with a thickness of 15 nm. Then, the siliconnitride film 112 is formed on the pad oxide film 111, for example, bylow pressure CVD (LP-CVD). The silicon nitride film 112 is formed, forexample, with a thickness of 160 nm.

In this example, a silicon nitride film/pad oxide film structure isused. Alternatively, a silicon nitride film/polysilicon film oramorphous silicon film/pad oxide film structure may be used.

Next, referring to FIG. 8, a resist mask (not shown) is formed on thesilicon nitride film 112, the resist mask having an opening at theposition corresponding to an element isolation region-forming region,and then, an opening 113 is formed by etching in the silicon nitridefilm 112 and the pad oxide film 111. In the etching process, forexample, a reactive ion etching (RIE) system, an electron cyclotronresonance (ECR) etching system, or the like may be used. After theprocessing, the resist mask is removed using an ashing apparatus or thelike.

Next, as shown in FIG. 9, using the silicon nitride film 112 as anetching mask, a first element isolation groove 114 and a second elementisolation groove 115 are formed in the semiconductor substrate 11. Inthe etching process, for example, an RIE system, an ECR etching system,or the like is used.

First, first etching for the second element isolation groove 115 and thefirst element isolation groove 114 in the peripheral circuit section andthe pixel section is performed. At this stage, the depth of each of thefirst and second element isolation grooves 114 and 115 is 50 to 160 nmin the peripheral circuit section and the pixel section.

Although not shown, a resist mask is formed on the pixel section, andsecond etching is performed such that the second element isolationgroove 115 is extended only in the peripheral circuit section. Thereby,the depth of the second element isolation groove 115 is set, forexample, at 0.3 μm only in the peripheral circuit section. Then, theresist mask is removed.

In such a manner, by forming the shallow first element isolation groove114 in the pixel section, it is possible to suppress white defects dueto etching damage, which is advantageous. By forming the shallow firstelement isolation groove 114, the effective area of the photoelectricconversion section is increased, and therefore, the saturation chargeamount is increased, which is advantageous.

Next, although not shown, a liner film is formed. The liner film isformed, for example, by thermal oxidation at about 800° C. to 900° C.The liner film may be a silicon oxide film, a nitrogen-containingsilicon oxide film, or a CVD silicon nitride film. The thickness of theliner film is about 4 to 10 nm.

Furthermore, although not shown, using a resist mask, ion implantationof boron (B) is performed on the pixel section in order to suppress darkcurrent. The ion implantation is performed, for example, at animplantation energy of about 10 keV and at a dosage of 1×10¹²/cm² to1×10¹⁴/cm². In the area surrounding the first element isolation groove114 in which the element isolation region is formed in the pixelsection, with an increase in the boron concentration, dark current ismore suppressed, and the action of parasitic transistors is moreprevented. However, if the boron concentration is excessively increased,the area for the photodiode constituting the photoelectric conversionsection decreases, and the saturation charge amount decreases.Therefore, the dosage is set in the range described above.

Next, as shown in FIG. 10, an insulating film is formed on the siliconnitride film 112 so as to fill the inside of each of the second elementisolation groove 115 and the first element isolation groove 114. Theinsulating film is formed, for example, by depositing silicon oxide byhigh-density plasma CVD.

Then, by removing an excess insulating film on the silicon nitride film112, for example, by chemical mechanical polishing (CMP), the insulatingfilm is left inside each of the second element isolation groove 115 andthe first element isolation groove 114, thereby forming the secondelement isolation region 15 and the first element isolation region 14.In the CMP process, the silicon nitride film 112 serves as a stopper.

Next, as shown in FIG. 11, in order to adjust the height of the firstelement isolation region 14 from the surface of the semiconductorsubstrate 11, the oxide film is wet-etched. The amount of etching of theoxide film is, for example, 40 to 100 nm.

Next, by removing the silicon nitride film 112 (refer to FIG. 10), thepad oxide film 111 is exposed. The silicon nitride film 112 is removed,for example, by wet etching using hot phosphoric acid.

Next, as shown in FIG. 12, using a resist mask (not shown) having anopening at the position corresponding to a p well-forming region, ionimplantation is performed through the remaining pad oxide film 111 toform a p well 121 in the semiconductor substrate 11. Channel ionimplantation is further performed. Then, the resist mask is removed.

Furthermore, using a resist mask (not shown) having an opening at theposition corresponding to an n well-forming region, ion implantation isperformed through the remaining pad oxide film 111 to form an n well 123in the semiconductor substrate 11. Channel ion implantation is furtherperformed. Then, the resist mask is removed.

The p well 121 is formed using boron (B) as an ion implantation species,at an implantation energy of, for example, 200 keV, and at a dosage of,for example, 1×10¹³ cm⁻². The channel ion implantation of the p well 121is performed using boron (B) as an ion implantation species, at animplantation energy of, for example, 10 to 20 keV, and at a dosage of1×10¹¹ cm⁻² to 1×10¹³ cm⁻².

The n well 123 is formed using, for example, phosphorus (P) as an ionimplantation species, at an implantation energy of, for example, 200keV, and at a dosage of, for example, 1×10¹³ cm⁻². The channel ionimplantation of the n well 123 is performed using, for example, arsenic(As) as an ion implantation species, at an implantation energy of, forexample, 100 keV, and at a dosage of 1×10¹¹ cm⁻² to 1×10¹³ cm⁻².

Although not shown, next, ion implantation for forming a photodiode isperformed on the photoelectric conversion section to thereby form ap-type region. For example, in the photoelectric conversionsection-forming portion, ion implantation of boron (B) is performed onthe surface of the semiconductor substrate, and ion implantation ofarsenic (As) or phosphorus (P) is performed on a deeper region tothereby form an n⁻-type region joined to the lower part of the p-typeregion. In such a manner, the photoelectric conversion section having apn junction is formed.

Next, as shown in FIG. 13, the pad oxide film 111 (refer to FIG. 12) isremoved, for example, by wet etching. Then, a thick gate insulating film51H for high voltage is formed on the semiconductor substrate 11. Thethickness thereof is set at about 7.5 nm for a transistor with a supplyvoltage of 3.3 V and about 5.5 nm for a transistor with a supply voltageof 2.5 V. Next, a resist mask (not shown) is formed on the thick gateinsulating film 51H for high voltage, and the thick gate insulating film51H formed in the low voltage transistor region is removed.

After the resist mask is removed, a thin gate insulating film 51L isformed in the low voltage transistor region on the semiconductorsubstrate 11. The thickness thereof is set at about 1.2 to 1.8 nm for atransistor with a supply voltage of 1.0 V. Simultaneously, a thin gateinsulating film (not shown) is also formed in the transistor-formingregion in the pixel section, the thin gate insulating film beingcomposed of an oxide film, an oxynitride film, or the like.

As the oxide film, in order to further reduce the gate leak, a hafniumoxide film, a zirconium oxide film, or the like may be used. As theoxynitride film, a silicon oxynitride film, a hafnium oxynitride film, azirconium oxynitride film, or the like may be used. In such a manner, ahigh dielectric film can be used.

Hereinafter, in the drawings, for convenience′ sake, the thickness ofthe thick gate insulating film 51H and the thickness of the thin gateinsulating film 51L are shown to be the same.

Next, as shown in FIG. 14A which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a photoelectric conversion section 12 is formed in thesemiconductor substrate 11. The photoelectric conversion section 12 isformed in the p well 125 (121) disposed in the semiconductor substrate11 in the pixel section 10, and includes a p-type region 12P and ann⁻-type region disposed thereunder.

Element isolation regions 16 are disposed in the semiconductor substrate11, the element isolation regions isolating an active region 15 in whichthe pixel transistor section is disposed from the photoelectricconversion section 12, isolating pixels from each other, and isolatingtransistors from each other in the peripheral circuit section 17. FIG.14A shows the element isolation region 16 which isolates thephotoelectric conversion section 12 from the active region 15, theelement isolation region 16 which isolates pixels from each other, andthe element isolation region 16 which isolates transistors from eachother in the peripheral circuit section 17 in that order from the left.Each of the element isolation regions 16 has, for example, a shallowtrench isolation (STI) structure.

A gate electrode-forming film 131 is formed on the semiconductorsubstrate 11 with the gate insulating films 51 (51H and 51L describedwith reference to FIG. 13) and a gate insulating film 20 therebetween.The gate electrode-forming film 131 is formed, for example, bydepositing polysilicon by LP-CVD. The thickness of the deposition film,which depends on the technology node, is 150 to 200 nm at the 90-nmnode.

Furthermore, in general, the thickness tends to decrease with node inorder not to increase the gate aspect ratio in view of processcontrollability.

Furthermore, in order to prevent gate depletion, silicon germanium(SiGe) may be used instead of polysilicon. The term “gate depletion”refers to the problem that as the thickness of the gate oxide filmdecreases, not only the effect of the physical thickness of the gateoxide film but also the effect of the thickness of the depletion layerin the gate plysilicon film becomes non-negligible, and the effectivethickness of the gate oxide film does not decrease, resulting in adecrease in the transistor performance.

Next, as shown in FIG. 14B which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, measures are taken to prevent gate depletion. First, aresist mask 141 is formed on the pMOS transistor-forming region, and thegate electrode-forming film 131 in the nMOS transistor-forming region isdoped with an n-type impurity. In the doping process, for example, ionimplantation of phosphorus (P) or arsenic (As) is performed. The ionimplantation dosage is about 1×10¹⁵/cm² to 1×10¹⁶/cm². Then, the resistmask 141 is removed.

Next, although not shown, a resist mask (not shown) is formed on thenMOS transistor-forming region, and the gate electrode-forming film 131in the pMOS transistor-forming region is doped with a p-type impurity.In the doping process, for example, ion implantation of boron (B), borondifluoride (BF₂), or indium (In) is performed. The ion implantationdosage is about 1×10¹⁵/cm² to 1×10¹⁶/cm². Then, the resist mask isremoved. FIG. 14B shows the state immediately before removing the resistmask 141.

The order of ion implantations is not limited to that described above,and the p-type impurity doping may be performed first. Furthermore, ineach of the ion implantation, in order to prevent the ion-implantedimpurity from passing through the gate insulating film, ion implantationof nitrogen (N₂) may be combined.

Next, as shown in FIG. 15A which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, an insulating film 132 is deposited on the gateelectrode-forming film 131, the insulating film 132 serving as a maskduring the gate processing. As the insulating film 132, for example, anoxide film or a nitride film is used. The thickness thereof is about 10to 100 nm.

Next, resist masks 142 for forming each of gate electrodes are formed onthe insulating film 132. The insulating film 132 is etched to form masksby reactive ion etching using the resist masks 142 as etching masks.Then, using the masks of the insulating film 132 as etching masks, thegate electrode-forming film 131 is etched.

As a result, as shown in FIG. 15B which includes a cross-sectional viewof the pixel section 10 and a cross-sectional view of the peripheralcircuit section 17, gate electrodes 21 and 22 of the MOS transistors inthe pixel section 10 and gate electrodes 52 of MOS transistors in theperipheral circuit section 17 are formed. FIG. 15B shows the gateelectrode 21 of the transfer transistor and the gate electrode 22 (22R)of the reset transistor. In the process of forming the gate electrodes22, although not shown, the gate electrode of the amplifier transistorand the gate electrode of the selection transistor are also formed.

As described with reference to FIG. 1, etc., in at least one gateelectrode 22 among the gate electrodes 22 of the transistors in thepixel transistor section 13, the gate width direction is oriented towardthe photoelectric conversion sections 12.

In each of the gate electrodes 22, at least a photoelectric conversionsection 12 side portion is disposed within and on the active region 15with the gate insulating film 20 therebetween.

Then, the resist masks 142 (refer to FIG. 15A) are removed, and theinsulating film 132 (refer to FIG. 15A) is removed by wet etching. FIG.15B shows the state after removing the resist masks 142 and theinsulating film 132.

Next, as shown in FIGS. 16A and 16B, each including a cross-sectionalview of the pixel section 10 and a cross-sectional view of theperipheral circuit section 17, LDD regions (not shown) of the MOStransistors, etc. in the peripheral circuit section 17 are formed.

First, as shown in FIG. 16A, a resist mask 143 having an opening at theposition corresponding to the PMOS transistor-forming region is formedby resist application, lithography, etc. Next, with respect to the PMOStransistor-forming region in the peripheral circuit section 17, pocketdiffusion layers (not shown) are formed in the semiconductor substrate11 at both sides of the gate electrode 52 (52P). The pocket diffusionlayers are formed by ion implantation, in which arsenic (As) orphosphorus (P) is used as an ion implantation species, and the dosage isset, for example, at 1×10¹²/cm² to 1×10¹⁴/cm².

Furthermore, LDD regions (not shown) are formed in the semiconductorsubstrate 11 at both sides of the gate electrode 52 (52P). The LDDregions are formed by ion implantation, in which, for example, borondifluoride (BF₂), boron (B), or indium (In) is used as an ionimplantation species, and the dosage is set, for example, at 1×10¹³/cm²to 1×10¹⁵/cm². Then, the resist mask 143 is removed. FIG. 16A shows thestate immediately before removing the resist mask 143.

Next, as shown in FIG. 16B, a resist mask 144 having an opening at theposition corresponding to the NMOS transistor-forming region in theperipheral circuit section 17 is formed by resist application,lithography, etc.

With respect to the NMOS transistors formed in the peripheral circuitsection 17, pocket diffusion layers (not shown) are formed in thesemiconductor substrate 11 at both sides of each of the gate electrodes52 (52N). The pocket diffusion layers are formed by ion implantation, inwhich, for example, boron difluoride (BF₂), boron (B), or indium (In) isused as an ion implantation species, and the dosage is set, for example,at 1×10¹²/cm² to 1×10¹⁴/cm².

Furthermore, LDD regions (not shown) are formed in the semiconductorsubstrate 11 at both sides of each of the gate electrodes 52 (52N). TheLDD regions are formed by ion implantation, in which, for example,arsenic (As) or phosphorus (P) is used as an ion implantation species,and the dosage is set, for example, at 1×10¹³/cm² to 1×10¹⁵/cm². Then,the resist mask 144 is removed. FIG. 16B shows the state immediatelybefore removing the resist mask 144.

Furthermore, before pocket ion implantation for NMOS transistors andPMOS transistors in the peripheral circuit section 17, in order tosuppress channeling in the implantation, pre-amorphization may beperformed, for example, by ion implantation of germanium (Ge). Inaddition, in order to reduce implantation defects which may causetransient enhanced diffusion (TED) or the like after the formation ofLDD regions, rapid thermal annealing (RTA) treatment at about 800° C. to900° C. may be performed.

Since LDD ion implantation is not performed on the pixel section 10, LDDregions are not formed under the sidewalls as shown in thecross-sectional structure of FIG. 1C.

Next, as shown in FIG. 17A which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a silicon oxide (SiO₂) film 134 is formed over the entiresurface of the pixel section 10 and the peripheral circuit section 17.The silicon oxide film 134 is a deposition film composed of non-dopedsilicate glass (NSG), LP-tetra ethyl ortho silicate (TEOS), or ahigh-temperature oxidation (HTO) film. The silicon oxide film 134 isformed, for example, with a thickness of 10 nm or less.

Next, as shown in FIG. 17B which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a silicon nitride film 135 is formed on the silicon oxidefilm 134. The silicon nitride film 135 is, for example, formed byLP-CVD. The thickness thereof is, for example, 50 nm or less.

The silicon nitride film 135 may be an ALD silicon nitride film formedby atomic layer deposition which can be performed at low temperature.

On the photoelectric conversion section 12 in the pixel section 10, thesilicon oxide film 134 beneath the silicon nitride film 135 moreprevents light reflection as the thickness of the silicon oxide film 134decreases, thus improving the sensitivity of the photoelectricconversion section 12.

Next, as necessary, a third-layer silicon oxide (SiO₂) film (not shown)is deposited on the silicon nitride film 135. This silicon oxide film isa deposition film composed of NSG, LP-TEOS, or a HTO film.

In this example, a sidewall-forming film 137 has a two-layer structureof silicon nitride film 135/silicon oxide film 134. As described above,the sidewall-forming film 137 may have a three-layer structure ofsilicon oxide film/silicon nitride film/silicon oxide film.

Next, as shown in FIG. 18A which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a resist mask 145 which covers the pixel section 10 isformed. Using the resist mask 145, the sidewall-forming film 137 isetched to thereby form sidewall insulation films 53 on the sidewalls ofeach of the gate electrodes 52.

It may be possible to decrease the number of process steps by etchingthe sidewall-forming film 137 to form the sidewall insulation films 53without forming the resist mask 145. However, in such a case, etchdamage easily occurs in the pixel section 10 during the processing ofthe sidewalls, and thus attention is necessary. When etching damageoccurs, dark current increases, which is a problem.

Then, the resist mask 145 is removed. FIG. 18A shows the stateimmediately before removing the resist mask 145.

Next, as shown in FIG. 18B which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a silicon oxide film 138 for forming the sidewalls is formedover the entire surface. The silicon oxide film 138 is a deposition filmcomposed of NSG, LP-TEOS, or a HTO film. The silicon oxide film 138 isformed, for example, with a thickness of 50 nm or less.

Next, as shown in FIG. 19A which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, the silicon oxide film 138 is etched back to form a sidewallinsulation film 23. In this step, in order to prevent damage due to theetch-back, the etch-back is stopped at the silicon nitride film 135.Thereby, it is possible to suppress dark current in the pixel section 10due to etch-back damage.

The sidewall insulation films 23 formed in the pixel section 10 eachinclude the silicon oxide film 134, the silicon nitride film 135, andthe silicon oxide film 138 formed on each sidewall of each of the gateelectrodes 21 and 22. The sidewall insulation films 53 each include thesilicon oxide film 134, the silicon nitride film 135, and the siliconoxide film 138 formed on each sidewall of each of the gate electrodes52. Some of the sidewall insulation films 23 (not shown) disposed onsidewalls parallel to the gate length direction of the gate electrodes22 extend over the boundary between the active region 15 and the elementisolation region 16 as shown in FIG. 1B, FIG. 3, etc.

Next, as shown in FIG. 19B which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a resist mask 146 having an opening at the positioncorresponding to the PMOS transistor-forming region is formed by resistapplication, lithography, etc. Using the resist mask 146, source/drainregions 54 (54P) and 55 (55P) are formed by ion implantation in the PMOStransistor-forming region of the peripheral circuit section 17. That is,the source/drain regions 54P and 55P are formed in the semiconductorsubstrate 11 at both sides of each gate electrode 52 (52P) with the LDDregions (not shown) therebetween. The source/drain regions 54P and 55Pare formed by ion implantation, in which, for example, boron (B) orboron difluoride (BF₂) is used as an ion implantation species, and thedosage is set, for example, at 1×10¹⁵/cm² to 1×10¹⁶/cm². Then, theresist mask 146 is removed. FIG. 19B shows the state immediately beforeremoving the resist mask 146.

Next, as shown in FIG. 20A which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a resist mask 147 having an opening at the positioncorresponding to the NMOS transistor-forming region in the peripheralcircuit section 17 is formed by resist application, lithography, etc.Using the resist mask 147, source/drain regions 54 (54N) and 55 (55N)are formed by ion implantation in the NMOS transistor-forming region ofthe peripheral circuit section 17. That is, the source/drain regions 54Nand 55N are formed in the semiconductor substrate 11 at both sides ofeach gate electrode 52 (52N) with the LDD regions (not shown)therebetween. The source/drain regions 54N and 55N are formed by ionimplantation, in which, for example, arsenic (As) or phosphorus (P) isused as an ion implantation species, and the dosage is set, for example,at 1×10¹⁵/cm² to 1×10¹⁶/cm². Then, the resist mask 147 is removed. FIG.20A shows the state immediately before removing the resist mask 147.

Next, as shown in FIG. 20B which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a resist mask 148 having an opening at the positioncorresponding to the well contact-forming region of the pixel section 10is formed by resist application, lithography, etc. Using the resist mask148, a contact region 126 is formed by ion implantation in the wellcontact-forming region of the pixel section 10. That is, the contactregion 126 is formed in the p well 125 of the pixel section 10, thecontact region 126 having a higher impurity concentration than the pwell 125. The contact region 126 is formed by ion implantation, in whichboron (B) or boron difluoride (BF₂) is used as an ion implantationspecies, and the dosage is set, for example, at 1×10¹⁵/cm² to1×10¹⁶/cm². Then, the resist mask 148 is removed. FIG. 20B shows thestate immediately before removing the resist mask 148.

Next, as shown in FIG. 21 which includes a cross-sectional view of thepixel section 10 and a cross-sectional view of the peripheral circuitsection 17, a resist mask 149 having an opening at the positioncorresponding to the pixel transistor section-forming region of thepixel section by resist application, lithography, etc. Using the resistmask 149, source/drain regions 24 and 25 are formed by ion implantationin the NMOS transistor-forming region of the pixel section 10. That is,the source/drain regions 24 and 25 are formed in the semiconductorsubstrate 11 at both sides of each gate electrode 22. The source/drainregions 24 and 25 are formed by ion implantation, in which, for example,arsenic (As) or phosphorus (P) is used as an ion implantation species,and the dosage is set, for example, at 1×10¹⁵/cm² to 1×10¹⁶/cm².

Simultaneously, a floating diffusion FD is formed in the semiconductorsubstrate 11 on one side of the gate electrode 21.

Then, the resist mask 149 is removed. FIG. 21 shows the stateimmediately before removing the resist mask 149.

The ion implantation may be performed at the same time as the ionimplantation for forming the source/drain regions 54N and 55N of eachNMOS transistors in the peripheral circuit section.

Next, activation annealing is performed on each of the source/drainregions. The activation annealing is performed, for example, at about800° C. to 1,100° C. The activation annealing may be performed, forexample, using a rapid thermal annealing (RTA) system, a spike-RTAsystem, or the like.

In the method of manufacturing a solid-state imaging device according tothe embodiment described above, among the transistors in the pixeltransistor section 13, at least one transistor in which the gate widthdirection of its gate electrode 22 is oriented toward the photoelectricconversion section 12 is formed such that a photoelectric conversionsection side portion of the gate electrode 22 is disposed within andabove the active region. Consequently, the size of the pixel transistorsection 13-forming region is reduced compared with the case whereprotruding portions of gate electrodes protrude over an elementisolation region according to the related art. That is, the size of thephotoelectric conversion section 12 can be increased by an areacorresponding to the area occupied by protruding portions of gateelectrodes formed so as to protrude over the element isolation regionaccording to the related art, and thus the formation area of thephotoelectric conversion section 12 can be increased.

Consequently, the saturation charge amount can be increased, which isadvantageous. Furthermore, since the gate capacitance of the pixeltransistor section 13 can be decreased, conversion efficiency can beincreased. Moreover, sensitivity can be improved.

Furthermore, since the gate electrodes 22R, 22A, and 22S do not extendover the element isolation region 16, the action of parasitictransistors can be prevented. Consequently, generation of dark currentcan be reduced, and high-quality images can be obtained.

Furthermore, the amplifier transistor TrA only may be formed such thatthe gate electrode 22A protrudes over the element isolation region 16 asin the related art. In such a case, the area of the photoelectricconversion section 12 can be increased relative to the related art andthe channel area of the amplifier transistor TrA can be increased.Therefore, it is possible obtain pixel characteristics in which randomnoise does not deteriorate.

Fifth Embodiment Second Example of Method of Manufacturing Solid-StateImaging Device

An example of a method of manufacturing a solid-state imaging deviceaccording to an embodiment of the present invention will be describedwith reference to FIG. 22 which includes cross-sectional views.

Basically, the same steps as those in the first example of the method ofmanufacturing a solid-state imaging device are carried out. After thestep described with reference to FIG. 16B, as shown in FIG. 22 whichincludes a cross-sectional view of the pixel section 10 and across-sectional view of the peripheral circuit section 17, a resist mask151 is formed so as to cover the photoelectric conversion section 12 andthe PMOS transistor-forming region of the peripheral circuit section 17.The resist mask 151 also covers the active region 15 including theboundaries between the element isolation regions 16 parallel to the gatelength direction of the gate electrode 22 and the active region 15.Because of this step, LDD regions are not formed under sidewallinsulation films which are formed on both sidewalls parallel to the gatelength direction of the gate electrode 22 in the subsequent step. Theresist mask 151 is formed by usual resist application and lithography.

Consequently, by performing ion implantation using the resist mask 151,LDD regions (not shown) are formed in the semiconductor substrate 11 onone side (opposite to the photoelectric conversion section 12 side) ofthe gate electrode 21 and on both sides of the gate electrode 22.Simultaneously, LDD regions (not shown) are formed in the semiconductorsubstrate 11 at both sides of the gate electrode 52N of the NMOStransistor. The LDD regions are formed by ion implantation, in which,for example, arsenic (As) or phosphorus (P) is used as an ionimplantation species, and the dosage is set, for example, at 1×10¹³/cm²to 1×10¹⁵/cm². Furthermore, pocket diffusion layers may be formed.

With respect to the MOS transistors formed in the pixel section 10, LDDregions may not be formed from the standpoint of reducing the number ofsteps. Alternatively, the ion implantation may be performed at the sametime as the ion implantation for forming LDD regions for MOS transistorsformed in the peripheral circuit section 17.

Then, the resist mask 151 is removed. FIG. 22 shows the stateimmediately before removing the resist mask 151.

In the second example of the method of manufacturing a solid-stateimaging device, the same working-effects as those in the first exampleof the method of manufacturing a solid-state imaging device can beobtained. Furthermore, since the LDD regions 26 and 27 are formed in thepixel transistor section 13, the electric field at the drain end islowered.

Sixth Embodiment Example of Imaging Apparatus

An example of an imaging apparatus according to a sixth embodiment ofthe present invention will be described with reference to FIG. 23 whichis a block diagram. Examples of the imaging apparatus include a videocamera, a digital still camera, and a mobile phone camera.

Referring to FIG. 23, an imaging apparatus 300 includes a solid-stateimaging device (not shown) as an imaging device 301. A focusing opticaldevice 302 which forms an image is provided on the light focusing sideof the imaging device 301. A signal processing device 303 is connectedto the imaging device 301, the signal processing device 303 including adriving circuit which drives the signal processing device 303, a signalprocessing circuit which processes signals photoelectrically convertedby the solid-state imaging device into an image, etc. Furthermore, theimage signals processed by the signal processing device can be stored byan image memory device (not shown). In such an imaging apparatus 300, asthe solid-state imaging device, any of the solid-state imaging devices1, 2, and 3 according to the embodiments of the present invention can beused.

In the imaging apparatus 300, since any of the solid-state imagingdevices 1, 2, and 3 having high sensitivity according to the embodimentsof the present invention is used, it is possible to record high-qualityimages, which is advantageous.

The structure of the imaging apparatus 300 is not limited to thatdescribed above. The embodiment of the present invention is applicableto any structure of an imaging apparatus as long as it includes asolid-state imaging device.

Each of the solid-state imaging devices 1, 2, and 3 may be formed as onechip or may be formed into a module in which the imaging device and asignal processing device or an optical system are packaged.

The term “imaging” not only refers to image taking during ordinaryshooting with camera, but also refers to, in the broad sense,fingerprint detection, etc.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2008-289670 filedin the Japan Patent Office on Nov. 12, 2008, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An imaging device, comprising: a plurality ofphotoelectric conversion elements; transistor elements including a resettransistor, an amplification transistor, and a selection transistor,wherein the plurality of photoelectric conversion elements share thereset transistor, the amplification transistor, and the selectiontransistor, and wherein an active region of the amplification transistorand an active region of the selection transistor are surrounded by anelement isolation region in a plan view; and a sidewall isolation filmon a side of a gate of the amplification transistor that is located overat least a first portion of the element isolation region in across-section view, and a sidewall isolation film on a side of a gate ofthe selection transistor that is located over at least a second portionof the element isolation region in the cross-section view.
 2. Theimaging device according to claim 1, wherein, for at least one of theamplification transistor and the selection transistor, the active regionis disposed under the gate, and wherein the sidewall isolation filmextends over a boundary between the active region and the elementisolation region.
 3. The imaging device according to claim 1, wherein,for at least one of the amplification transistor and the selectiontransistor, the active region is disposed under the gate, and thesidewall isolation film is on both sides of the gate parallel to a gatelength direction and the sidewall isolation film extends over a boundarybetween the active region and the element isolation region on the bothsides of the gate.
 4. The imaging device according to claim 1, furthercomprising a floating diffusion region, wherein the floating diffusionregion is disposed between the plurality of photoelectric conversionelements.
 5. The imaging device according to claim 4, wherein thetransistor elements include a transfer transistor having a transfergate, and the transfer gate has a convex portion that extends towardsthe floating diffusion region.
 6. The imaging device according to claim1, wherein a p-type region is disposed at a surface of each of theplurality of photoelectric conversion elements.
 7. The imaging deviceaccording to claim 2, wherein source/drain regions associated with theat least one of the amplification transistor and the selectiontransistor are disposed in the active region, and wherein thesource/drain regions are separated from each other.
 8. The imagingdevice according to claim 1, wherein an element isolation regioncomprises shallow trench isolation.
 9. The imaging device according toclaim 1, wherein an area of the gate of the amplification transistor islarger than that of the gate of the reset transistor.
 10. The imagingdevice according to claim 1, wherein an area of the gate of theamplification transistor is larger than that of the gate of theselection transistor.
 11. The imaging device according to claim 1,wherein an area of the gate of the amplification transistor is largerthan that of the gate of the reset transistor and the gate of theselection transistor.
 12. The imaging device according to claim 1,further comprising: a semiconductor substrate including the plurality ofphotoelectric elements, and a gate insulating film, wherein the gateinsulating film is disposed between the semiconductor substrate and atleast one of the transistor elements.
 13. The imaging device accordingto claim 1, wherein the sidewall isolation film of at least one of thegate of the amplification transistor and the gate of the selectiontransistor is selected from the group consisting of silicon oxide,silicon nitride, and combinations thereof.
 14. The imaging deviceaccording to claim 1, wherein an active region of the reset transistoris surrounded by the element isolation region in the plan view, andwherein a sidewall isolation film on a side of a gate of the resettransistor is located over at least a third portion of the elementisolation region in the cross-section view.
 15. An electronic apparatus,comprising: an imaging device, comprising: a plurality of photoelectricconversion elements; transistor elements including a reset transistor,an amplification transistor, and a selection transistor, wherein theplurality of photoelectric conversion elements share the resettransistor, the amplification transistor, and the selection transistor,and wherein an active region of the amplification transistor and anactive region of the selection transistor are surrounded by an elementisolation region in a plan view; and a sidewall isolation film on a sideof a gate of the amplification transistor that is located over at leasta first portion of the element isolation region in a cross-section view,and a sidewall isolation film on a side of a gate of the selectiontransistor that is located over at least a second portion of the elementisolation region in the cross-section view.
 16. The electronic apparatusaccording to claim 15, wherein, for at least one of the amplificationtransistor and the selection transistor, the active region is disposedunder the gate, and wherein the sidewall isolation film extends over aboundary between the active region and the element isolation region. 17.The electronic apparatus according to claim 15, wherein, for at leastone of the amplification transistor and the selection transistor, theactive region is disposed under the gate, and the sidewall isolationfilm is on both sides of the gate parallel to a gate length directionand the sidewall isolation film extends over a boundary between theactive region and the element isolation region on the both sides of thegate.
 18. The electronic apparatus according to claim 15, furthercomprising a floating diffusion region, wherein the floating diffusionregion is disposed between the plurality of photoelectric conversionelements.
 19. The electronic apparatus according to claim 18, whereinthe transistor elements include a transfer transistor having a transfergate, and the transfer gate has a convex portion that extends towardsthe floating diffusion region.
 20. The electronic apparatus according toclaim 15, wherein a p-type region is disposed at a surface of each ofthe plurality of photoelectric conversion elements.
 21. The electronicapparatus according to claim 16, wherein source/drain regions associatedwith the at least one of the amplification transistor and the selectiontransistor are disposed in the active region, and wherein thesource/drain regions are separated from each other.
 22. The electronicapparatus according to claim 15, wherein an element isolation regioncomprises shallow trench isolation.
 23. The electronic apparatusaccording to claim 15, wherein an area of the gate of the amplificationtransistor is larger than that of the gate of the reset transistor. 24.The electronic apparatus according to claim 15, wherein an area of thegate of the amplification transistor is larger than that of the gate ofthe selection transistor.
 25. The electronic apparatus according toclaim 15, wherein an area of the gate of the amplification transistor islarger than that of the gate of the reset transistor and the gate of theselection transistor.
 26. The electronic apparatus according to claim15, further comprising: a semiconductor substrate including theplurality of photoelectric elements, and a gate insulating film, whereinthe gate insulating film is disposed between the semiconductor substrateand at least one of the transistor elements.
 27. The electronicapparatus according to claim 15, wherein the sidewall isolation film ofat least one of the gate of the amplification transistor and the gate ofthe selection transistor is selected from the group consisting ofsilicon oxide, silicon nitride, and combinations thereof.
 28. Theelectric apparatus according to claim 15, wherein an active region ofthe reset transistor is surrounded by the element isolation region inthe plan view, and wherein a sidewall isolation film on a side of a gateof the reset transistor is located over at least a third portion of theelement isolation region in the cross-section view.